Noxious Weeds

Noxious weeds are non-native plants that displace native plants or out-compete native plants for soil moisture and degrade natural habitat. Many noxious weeds are undesirable to cattle and wildlife, and can even be toxic, thereby reducing available forage habitat. It is important to manage noxious weeds in our area through identification, prevention and control of infestations.

Noxious weeds can be introduced through seeding, as ornamental escapes or can establish in disturbed areas (roadsides, overgrazed pastures, construction areas) as well as riparian corridors and wetlands. To control or prevent infestations and educate landowners, the state-wide Colorado Noxious Weed Act (35-5.5 CRS) was established to identify a noxious weed list and prioritized management goals. The state’s noxious weeds are grouped into three different lists, A, B and C. For a current list of those plants, please click here. This categorical listing of a noxious weed plant as A, B or C will dictate whether it is to be eradicated, contained or controlled.

Top five noxious weeds in Castle Rock

Several types of noxious weeds have been identified as the most undesirable, unwanted or priority for control in Douglas County.

Diffuse Knapweed

List B – to be eliminated or suppressed depending on the infestation

Native to the Mediterrean area

Tends to invade disturbed or overgrazed areas and roadsides

One plant can produce 18,000 seeds that may remain dormant for years but still be viable

Also known to outcompete native plants by releasing a chemical in the soil that suppresses other plant growth

Control best accomplished by early detection and eradication or multiple management strategies

Learn more about Dalmation Toadflax

Leafy Spurge

List B – to be eliminated or suppressed depending on the infestation

Native to central and southern Europe

Long-living creeping perennial that spreads by seed but also has extensive root system that makes control difficult

A management scheme that combines control methods over four to five years is recommended

Learn more about Leafy Spurge

Myrtle Spurge

List A – must be eradicated on all property

also called "donkey tail" or "creeping spurge"

drought-tolerant perennial native to Eurasia, first introduced to North America as an ornamental

considered a noxious weed because it is aggressive and proliferates easily, outcompetes native plants, and has toxic milky sap

Replacements for Myrtle Spurge

Colorado Four o'clock (Mirabilis multiflora)

Sulphur-flower Buckwheat (Eriogonum umbellatum)

Kinnikinnick (Arctostaphylos uva-ursi)

Creeping Barberry (Mahonia repens)

Four-nerve Daisy (Tetraneuris acaulis)

Tufted Evening Primrose (Oenothera caespitosa)

Learn more about Myrtle Spurge

Management

Noxious weeds can be managed by using a combination of control methods including mechanical, cultural, biological, preventive and chemical, but since they grow or spread differently, not all methods will be effective on all weeds. Refer to the Colorado Department of Agriculture for required controls. Consult with Douglas County Weed Control for specific recommendations for eradication, containment or control. It is important to properly identify noxious weeds and use diverse control methods to reduce or eradicate infestations.

The Town Parks and Recreation Department, Public Works and Castle Rock Water utilizes integrated management techniques to actively manage noxious weeds on Town-owned properties, including parks, trails, open space areas, well sites and public right of ways. Mowing, hand pulling, native grass restoration, herbicides and biological control agents are all examples of integrated management techniques used by the Town.

The Town does not spray herbicides indiscriminately but rather uses a spot spray approach for heavy infestations of weeds and only use low-toxicity chemicals that are not restricted. Additionally, the Town has found success utilizing releases of biological control agents, seedhead and root-boring weevils, to control large infestations of Diffuse Knapweed on Town-owned open space properties.

Castle Rock residents are encouraged, and required by both Town Municipal Code and state statute, to control noxious weeds on their property.